Longitudinal Magnetic Field Research Articles

Study of the evolution of pulsed plasma under an external longitudinal magnetic field

An experimental study on the role of an external longitudinal magnetic field on the characteristics changes of pulsed plasma stream, produced in argon medium, is carried out at different time spans of its evolution. The spectroscopic observations are time integrated and are carried out at different times of plasma formation for pulsed discharge. This study gives insights into the recombination and diffusion phase of the plasma species in the presence of the magnetic field. The transition of plasma species from a dominant recombination phase to a diffusional phase is well revealed by the density profile during the time evolution. Moreover, the decrease in electron temperature and the increase in electron excitation temperature explain the energy transfer to electrons due to metastable quenching, and the system gradually approaches equilibrium. The magnetic field also affects the transitions of the ionized argon population between different energy levels. It is found that faster decay occurs for transitions of different plasma species to non-metastable states, while the populations of metastable states exist for a longer time. In addition, the time-resolved morphology changes of the plasma stream are also observed by high speed imaging, which shows the flow structure of the plasma stream at different time frames. The imaging of the plasma stream evolution shows the initial ejection of the plasma sheet from the electrode assembly, its detachment, the steady flow, and gradually its nature of dying out.

Physical Properties of a Low-Power Helicon Source Operating on a High-Frequency Discharge with a Capacitive Component

The results of an experimental study of a low-power RF plasma source placed in a longitudinal magnetic field (helicon thruster), when it operates on a capacitive RF discharge and inductive RF discharges with a capacitive component, are presented. A significant dependence of the characteristics of the ion and electron fluxes of the source on the induction of a constant magnetic field is shown. The fundamental applicability of capacitive RF discharge as a working process in the studied plasma source is demonstrated. It is shown that the increase in the average energy of ions in the flow at the outlet of the source with the appearance of the capacitive component of the discharge is slight.

MI-Sensor Element Features and Estimation of Penetration Depth and Magnetic Permeability by Magnetoresistance and Magnetoreactance of CoFeSiB Amorphous Wires

The magnetoimpedance (MI) of amorphous soft magnetic Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">68.15</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4.35</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12.5</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sub> wires produced by the in-rotating water quenching technique was systematically studied. The behavior of the MI-element designed for magnetic sensors was examined in an external longitudinal dc magnetic field in the low-frequency range (f ≤ 1 MHz) and at the beginning of the intermediate frequency range (2 MHz ≤ f ≤ 5 MHz). A critical frequency of about 5 kHz - 7 kHz was observed with an initial increase in the MI effect. A maximum MI ratio of 334% was recorded at 0.95 MHz in a magnetically saturated MI-element. The intermediate frequency range is explored using the magnetoresistive - MR and magnetoreactive - MX components of magnetoimpedance Z. The MI anisotropy field profile occurs in the MHz operating frequency range with values increasing up to 25 A/m, exhibiting frequency dependence. The magnetic penetration depth was calculated using experimental magnetoresistance data, and the values obtained were about 3 μm - 4 μm for 5 MHz, showing a saturation trend. The magnetic permeability is analyzed in the framework of the electromagnetic classical high-limit model of a cylinder, which includes penetration depth and magnetoreactance. In our experiments and calculations, the classical high limit is satisfied in the operating frequency range of a few MHz. The magnetic permeability peak value is about 35% lower than the comparable data of amorphous CoFeNiMoSiB glass-coated microwires.

INVESTIGATION OF THE MAGNETIC FIELD FROM OBSERVATIONS OF THE OH MASER IN THE G10.624–0.385 STAR FORMATION REGION

The results of a study of the variability of maser emission in OH lines in the 18 cm range in the G10.624–0.385 star formation region from monitoring data performed at the Large Radio Telescope in Nançay (France) in 2008–2023 are presented. It is obtained that for a Zeeman pair in line 1667 MHz splitting (about 1.96 km/s) and, consequently, the magnitude of the longitudinal magnetic field have been stable for more than 25 years. In the satellite lines of 1612 and 1720 MHz, broadband absorption and emission are observed, respectively. Mirrored The profiles of the OH 1612 and 1720 MHz satellite lines indicate that the levels of the corresponding transitions are pumped by IR radiation from a source immersed in a magnetized molecular cloud around the OH maser. Spatial identification of details in both main lines is carried out. It is found that the transverse magnetic field is directed mainly along some organized structure in the form of an arc.

INVESTIGATION OF OH 18 CM MASER EMISSION AND MAGNETIC FIELD IN THE S128 STAR FORMATION REGION

The results of a study of the variability of OH maser emission in the lines of 18 cm in the S128 star formation region from monitoring data in 2007–2022 at the Large Radio Telescope in Nançay (France) are presented. Maser emission was observed in the main line of 1665 MHz during the entire monitoring, and only short-term emission was observed in the satellite lines of 1612 and 1720 MHz. For the four strongest features in the 1665 MHz line, the variability of the positional angle of linearly polarized emission was found. The dependence of the angle on the radial velocity to some extent resembles a limited sinusoid, which may be due to the existence of an organized spatial structure of maser spots and the associated transverse magnetic field. For two Zeeman pairs in the 1612 MHz line having similar radial velocities (–75.344/–75.236 and –74.980/–74.903 km/s), the detected splits have opposite signs and, therefore, opposite directions of the longitudinal magnetic field. The directions of the transverse magnetic field vectors are also determined for these features. Apparently, the magnetic field is swirling and is associated with a swirling molecular outflows of matter.

Magnetic Fields and Fragmentation of Filaments in the Hub of California-X

We present 850 μm polarization and C18O (3-2) molecular line observations toward the X-shaped nebula in the California molecular cloud using James Clerk Maxwell Telescope (JCMT)’s SCUBA-2/POL-2 and HARP instruments. The 850 μm emission shows that the observed region includes two elongated filamentary structures (Fil1 and Fil2) having chains of regularly spaced cores. We measured the mass per unit length of the filaments and found that Fil1 and Fil2 are thermally super- and subcritical, respectively, but both are subcritical if nonthermal turbulence is considered. The mean projected spacings () of the cores in Fil1 and Fil2 are 0.13 and 0.16 pc, respectively. is smaller than 4× the filament width expected in the classical cylinder fragmentation model. The large-scale magnetic field orientations shown by Planck are perpendicular to the long axes of Fil1 and Fil2, while those in the filaments obtained from the high-resolution polarization data of JCMT are disturbed, but those in Fil1 tend to have longitudinal orientations. Using the modified Davis–Chandrasekhar–Fermi method, we estimated the magnetic field strengths (B pos) of the filaments, which are 110 ± 80 and 90 ± 60 μG, respectively. We calculated the gravitational, kinematic, and magnetic energies of the filaments, and found that the fraction of magnetic energy is larger than 60% in both filaments. We propose that the dominant magnetic energy may lead the filament to be fragmented into aligned cores as suggested by Tang et al., and the shorter core spacing can be due to a projection effect via the inclined geometry of the filaments or due to nonnegligible longitudinal magnetic fields in the case of Fil1.

Nonlinear nonlocal damped free and forced vibrations of piezoelectric SWCNTs under longitudinal magnetic field due to surface effects using a two steps perturbation method

In the present work, damped free and forced vibrations of single-walled piezoelectric carbon nanotubes under longitudinal magnetic field due to surface effects surrounded on a non-linear viscoelastic medium using the nonlocal Euler-Bernoulli beam theory and multiple time scales method are investigated. Lorentz force equation is used to obtain the vertical force due to the applied voltage to the system. The surface effects as well as a combinational non-linear viscoelastic foundation are considered, and finally, the dynamic equilibrium equations are used, and non-linear equations of motion are extracted. In the following, the Galerkin and multiple time scales methods are used, and finally, analytical solutions are extracted as the non-linear free and forced vibrational responses of the system. The relevant coefficients of the extracted analytical solutions are discovered for two both simple support (S-S) and clamped (C-C) boundary conditions. In the following, , and the effects of the different parameters such as non-local parameter as well as electric-magnetic fields, effect of hardness-linear damping parameters of nonlinear considered viscoelastic foundation, applied magnetic field, base modes for different forms considering surface effects, and etc. will be studied. As one the results of this study, the presence of a non-local parameter has increased the curvature deviation to the right and the stiffening effect. In other words, the non-local parameter is a factor to increase the nonlinear effect of the system. Also, it is predictable that as the load affect position moves away from the center of the single-walled piezoelectric carbon nanotube toward the supports, the amplitude of the dynamic response decreases significantly, and this relative reduction is greater for the C-C boundary condition than for the S-S boundary condition. It is also important to note that the location of the load has no effect on the rate of deviation of the curve peak, and the degree of nonlinearity of the vibrational response of the system.

Deep neural networks of solar flare forecasting for complex active regions

Solar flare forecasting is one of major components of operational space weather forecasting. Complex active regions (ARs) are the main source producing major flares, but only a few studies are carried out to establish flare forecasting models for these ARs. In this study, four deep learning models, called Complex Active Region Flare Forecasting Model (CARFFM)-1, −2, −3, and −4, are established. They take AR longitudinal magnetic fields, AR vector magnetic fields, AR longitudinal magnetic fields and the total unsigned magnetic flux in the neutral line region, AR vector magnetic fields and the total unsigned magnetic flux in the neutral region as input, respectively. These four models can predict the production of M-class or above flares in the complex ARs for the next 48 h. Through comparing the performance of the models, CARFFM-4 has the best forecasting ability, which has the most abundant input information. It is suggested that more valuable and rich input can improve the model performance.

Preparation and characterization of CMT wire arc additive manufacturing Al-5%Mg alloy depositions through assisted longitudinal magnetic field

The presence of hydrogen pores and cracks has been identified as the leading cause of the poor mechanical properties of the cold metal transfer (CMT) wire arc additive manufacturing aluminum alloy depositions. A comparison of additive specimens with porosity defects, microstructure and mechanical properties was conducted through the application of magnetic field-assisted CMT wire arc additive manufacturing Al-5%Mg alloy depositions. The results showed that the longitudinal direct-current (DC) magnetic field affected the flow of liquid metal by changing the arc morphology, which improved the forming quality, microstructure and mechanical properties of the arc additive manufacturing Al-5%Mg alloys. It can be concluded that the longitudinal DC magnetic field plays a significant optimized role in the generation of porosity defects and forming morphology in the additive specimens. At an excitation current of 2A, the average microhardness is 81.42 HV, which is 11.28 % higher than that of the additive specimen without an applied magnetic field. The application of a longitudinal DC magnetic field effectively reduced the grain size, increased the number of large-angle grain boundaries, reduced the grain orientation difference, and made the grain boundaries less prone to cracking, thereby enhancing the microhardness and tensile properties of the additive specimens.

Static pull-in analysis of the cantilever and clamped FG-microswitches in presence of the longitudinal magnetic field based on the modified couple stress theory

Static pull-in analysis of the cantilever and clamped FG-microswitches in presence of the longitudinal magnetic field based on the modified couple stress theory

ACCELERATION OF COMPENSATED HIGH-CURRENT ION BEAM WITH CUSP MAGNETIC ELECTRON INSULATION IN THE ACCELERATING GAP AND SUBSEQUENT COMPENSATION WITH AN ELECTRON BEAM

2.5D simulation of the process of the magnetic isolation of electrons and the acceleration of ions when injecting a high-current ion beam, compensated by an electron beam, into a magnetic cusp with an accelerating gap, followed by its re-compensation by another electron beam and transportation along the drift region with a longitudinal magnetic field, was carried out. The dependence of the characteristics of the accelerated and compensated ion beam at the drift region exit upon the set of initial parameters of the ion and electron beams and the values of the magnetic and accelerating electric fields was considered.

Linear and circular dichroisms of cholesteric liquid crystals in a longitudinal external magnetic field

ABSTRACT We investigated the properties of linear and circular dichroisms of cholesteric liquid crystal layer in external static magnetic field directed along helix axis. We showed that when the direction of light propagation and the direction of external magnetic field coincide, increasing the latter magnitude leads to a decrease in the linear dichroism, whereas when these directions are opposite, increasing the external magnetic field ( B e x t ) magnitude leads an increase in the linear dichroism. The presence of external magnetic field leads to the shift of circular dichroism curves both along wavelength axis and along dichroism axis. Then, we investigated the peculiarities of dichroism dependencies on B e x t for different wavelengths of incident light. We compared the dependence of circular dichroism on B e x t for a magnetically active cholesteric liquid crystal layer and an isotropic magnetically active layer and showed that while these dependencies are similar for wavelengths away from the photonic band gap, diffraction significantly affects these dependencies for wavelengths near and inside the photonic band gap. We investigated the evolution of spectra of linear and circular dichroisms at the change in B e x t , too. The results obtained can find application in the design of innovative polarised optoelectronic devices.

Effect of a longitudinal magnetic field on arc motion and joint structure of a hollow stud

Given the non-uniform melting of the end face of a joint and the local non-fusion of the joint in large-diameter hollow stud welding, to research the law of arc motion, the joint-forming quality, weld microstructure and mechanical properties in the process of hollow stud welding propelled by a longitudinal magnetic field were investigated in this study. The results reveal that under the influence of a longitudinal magnetic field, the arc on the end of a stud is affected by the Lorentz force and spirals downward. In the welding process, with an increase in magnetic field intensity, the arc uniformly burns the stud end face, preventing local non-fusion and resulting in a well-shaped joint. Under the action of magnetic field stirring, eutectoid ferrite is broken, the content of eutectoid ferrite and bainite is diminished, the nucleation barrier is reduced and the grain is refined. Under the action of a longitudinal magnetic field, the shear strength of the hollow stud welded joint rises to 312 MPa, surpassing the strength of a joint welded without a magnetic field.

Near-IR and optical radial velocities of the active M dwarf star Gl 388 (AD Leo) with SPIRou at CFHT and SOPHIE at OHP

Context. The search for extrasolar planets around the nearest M dwarfs is a crucial step toward identifying the nearest Earth-like planets. One of the main challenges in this search is that M dwarfs can be magnetically active and stellar activity can produce radial velocity (RV) signals that could mimic those of a planet. Aims. We aim to investigate whether the 2.2-day period observed in optical RVs of the nearby active M dwarf star Gl 388 (AD Leo) is due to stellar activity or to a planet that corotates with the star as suggested in the past. Methods. We obtained quasi-simultaneous RVs of Gl 388 from 2019 to 2021 with SOPHIE, the optical échelle spectrograph (R ~75k) at the Observatoire de Haute-Provence in France, and RV and Stokes V measurements with SPIRou, the near-infrared spectropolarimeter at the Canada France Hawaii Telescope (R ~70k). Results. The SOPHIE RV time series (precision of 3–5 m s−1 per visit) displays a periodic signal with a 2.23 ± 0.01 day period and 23.6 ± 0.5 m s−1 amplitude, which is consistent with previous HARPS observations obtained in 2005–2006. The SPIRou RV time series (precision of 2 ms−1 per visit) is flat at 5 ms−1 rms and displays no periodic signals. RV signals of amplitude higher than 5.3 m s−1 at a period of 2.23 days can be excluded with a confidence level higher than 99%. Using the modulation of the longitudinal magnetic field (Bℓ) measured with SPIRou as a proxy of stellar rotation, we measure a rotation period of 2.2305 ± 0.0016 days. Conclusions. SPIRou RV measurements provide solid evidence that the periodic variability of the optical RVs of Gl 388 is due to stellar activity rather than to a corotating planet. The magnetic activity nature of the optical RV signal is further confirmed by the modulation of Bℓ with the same period. The SPIRou campaign on Gl 388 demonstrates the power of near-infrared RV to confirm or infirm planet candidates discovered in the optical around active stars. Our SPIRou observations additionally reiterate how effective spectropolarimetry is at determining the stellar rotation period from the variations of Bℓ.

Effective field theory study of bond dilution effects on transverse Ising antiferromagnet in a random longitudinal magnetic field

Effective field theory study of bond dilution effects on transverse Ising antiferromagnet in a random longitudinal magnetic field

Electromagnetic design study of a superconducting longitudinal gradient bend magnet based on the HALF storage ring

The National Synchrotron Radiation Laboratory is planning to build a 2.2 GeV diffraction-limited storage ring, the Hefei Advanced Light Facility (HALF), with a 6BA lattice structure and a large number of longitudinal gradient bends (LGBs). In order to increase the radiated photon energy to the hard X-ray band and to reduce the natural emittance, a superconducting longitudinal gradient bend (SLGB) magnet is planned to be used on HALF in the future, which requires a magnetic field integral of 0.40 T·m over a length of 0.46 m and a peak field of about 5 T. A SLGB has many structural parameters, such as the geometric parameters of the superconducting coils and the thickness of the yoke, etc. Their influence on the magnetic field distribution has been studied, although the computation of the 3D magnet model is very slow. Considering the longitudinal field variation, the vertical gap limitation, the field homogeneity requirement and the critical current of the superconducting wire, a method is developed to simplify the 3D magnet simulation by a corresponding 2D model, so that the longitudinal magnetic field profile of a 3D model can be approximately calculated in a 2D model with faster speed. Due to the faster calculation speed of 2D models, a Mathematica-based optimization program is developed and relatively good structural parameters for the HALF SLGB are found by the program. The simulation results show that the physical design requirements can be well met. The electromagnetic design for the HALF SLGB magnet is based on the current JC level of NbTi superconductor due to its excellent mechanical performance.

Airy transform of an electron Landau state in a longitudinal constant magnetic field

In this article, a relationship between the electron beams in a longitudinal constant magnetic field and light beams in a parabolic refractive index distribution medium is revealed and demonstrated analytically. We propose a new method to work out the properties of the singularity in that analytical expression and have a discussion on some universal features of electron beams in a longitudinal constant magnetic field. Based on the theories above, we introduce a new type of structured electron beams, which is the Airy transform of electron Landau states (ATLSs). We not only study the dynamic of ATLSs and the magnetic field analytically and numerically but also carry out the movement of centroid and the dual auto-focusing property of ATLSs. Moreover, we have a discussion on the influence on ATLSs of Airy control parameters and the parameters of electron Landau states.

The Behavior of Bp Si Stars in the Far UV—Paper V: HD 92664

The analysis of spectra of the B8 Si-rich HD 92664 recorded by the SWP camera on board the International Ultraviolet Explorer reveals variations of the far-ultraviolet spectral energy distribution shortwards of 1700 Å over a time interval of about 2 months. In contrast, the mid-UV flux does not vary which suggests that changes of the silicon continuous and line opacity are the cause of the variations. The iron-peak elements, chromium, manganese and iron play a lesser role than silicon in these variations. Phased on previous ephemeris, the FUV minimum occurs at the rotational phase, ϕ = 0.0, which corresponds to maximum light in the V-band and minimum longitudinal magnetic field.

Stability of a dielectric rectangular plate in a longitudinal magnetic field in the presence of a supersonic flow field

Stability of a dielectric rectangular plate in a longitudinal magnetic field in the presence of a supersonic flow field

An Efficient, Time‐Dependent High Speed Stream Model and Application to Solar Wind Forecasts

AbstractPredicting space weather effects of the solar wind requires knowing the location and properties of any embedded high speed streams (HSSs) or stream interactions regions (SIRs) that form as the fast solar wind catches up to slow preceding wind. Additionally, this background solar wind affects the evolution of coronal mass ejections. We present the Mostly Empirical Operation Wind with a High Speed Stream (MEOW‐HiSS) model, which runs nearly instantaneously. This model is derived from magnetohydrodynamic (MHD) simulations of an idealized HSS emanating from a circular coronal hole. We split the MHD HSS radial profiles into small regions well‐described by simple functions (e.g., flat, linear, exponential, sinusoidal) that can be constrained using the MHD values. We then determine how the region boundaries and the constraining values change with CH area and the radial distance of the HSS front. MEOW‐HiSS only requires this area and distance to reproduce the corresponding radial profile with an error of less than 10% for most parameters. MEOW‐HiSS produces profiles at any subsequent times with almost no loss in accuracy. We compare MEOW‐HiSS results to four HSS observed in situ at 1 au. We present a method for determining MEOW‐HiSS inputs from extreme ultra‐violet images and use these values to hindcast the observed cases. We find average accuracies of 2.8 cm−3 in the number density (50% error over the full profile), 56.7 km/s in the radial velocity (10%), 2.2 nT in the absolute radial magnetic field (50%), 1.6 nT in the absolute longitudinal magnetic field (50%), and 7 × 104 K in the temperature (50%).